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<chrono>: Replace an elaborate table with a switch #5905

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Merged
Stephan T. Lavavej (StephanTLavavej) merged 1 commit into from
Nov 27, 2025
Merged

<chrono>: Replace an elaborate table with a switch #5905

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79 changes: 35 additions & 44 deletions stl/inc/chrono
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Original file line number Diff line number Diff line change
Expand Up @@ -5353,61 +5353,52 @@ namespace chrono {
if (_Spec._Type != '\0' && !_Is_valid_type<_Ty>(_Spec._Type)) {
_STD _Throw_format_error("Invalid type.");
}
_Check_modifier(_Spec._Type, _Spec._Modifier);

if (!_Valid_modifier(_Spec._Type, _Spec._Modifier)) {
_STD _Throw_format_error("Incompatible modifier for type");
}
}

return _Res_iter;
}

enum _Allowed_bit : uint8_t { _E_mod = 1, _O_mod = 2, _EO_mod = _E_mod | _O_mod };

struct _Table_entry {
char _Type;
_Allowed_bit _Allowed;
};

static constexpr _Table_entry _Table[] = {
{'c', _E_mod},
{'C', _E_mod},
{'d', _O_mod},
{'e', _O_mod},
{'H', _O_mod},
{'I', _O_mod},
{'m', _O_mod},
{'M', _O_mod},
{'S', _O_mod},
{'u', _O_mod},
{'U', _O_mod},
{'V', _O_mod},
{'w', _O_mod},
{'W', _O_mod},
{'x', _E_mod},
{'X', _E_mod},
{'y', _EO_mod},
{'Y', _E_mod},
{'z', _EO_mod},
};

static constexpr void _Check_modifier(const char _Type, const char _Modifier) {
static constexpr bool _Valid_modifier(const char _Type, const char _Modifier) {
// N5014 [tab:time.format.spec] lists modified commands.
if (_Modifier == '\0') {
return;
return true;
}

const _Allowed_bit _Mod = _Modifier == 'E' ? _E_mod : _O_mod;
_STL_INTERNAL_CHECK(_Modifier == 'E' || _Modifier == 'O');

#ifdef _M_CEE // TRANSITION, VSO-1664341
constexpr auto _Get_table_entry_type = [](const _Table_entry& _Entry) { return _Entry._Type; };
#else // ^^^ workaround / no workaround vvv
constexpr auto _Get_table_entry_type = &_Table_entry::_Type;
#endif // ^^^ no workaround ^^^
switch (_Type) {
case 'c':
case 'C':
case 'x':
case 'X':
case 'Y':
return _Modifier == 'E';

if (auto _It = _RANGES find(_Table, _Type, _Get_table_entry_type); _It != _STD end(_Table)) {
if (_It->_Allowed & _Mod) {
return;
}
}
case 'd':
case 'e':
case 'H':
case 'I':
case 'm':
case 'M':
case 'S':
case 'u':
case 'U':
case 'V':
case 'w':
case 'W':
return _Modifier == 'O';

_STD _Throw_format_error("Incompatible modifier for type");
case 'y':
case 'z':
return true;

default:
return false;
}
}

template <class _Ty>
Expand Down